An extrusion apparatus or head used to make a marbled profile of a thermoplastic material is connectable to a screw press or extruder with at least one screw shaft and with an extruder housing. A thermoplastic marbling material having one color is mixed with a thermoplastic base material of another different color to produce a marbled thermoplastic product.
This extrusion apparatus or head comprises an extrusion apparatus housing, a central passage for receiving the thermoplastic base material which connects to the screw shaft and a shaping outlet. The extrusion apparatus housing has at least one injector cavity in which is mounted an injection device for feeding in the thermoplastic marbling material. It is understood that the thermoplastic marbling material is specially prepared and fed to the injection device for feeding it in. Generally this preparation occurs in a separate extruder.
In the known extrusion apparatus see (British Patent Specification 1,586,010) the injection device for feeding in the thermoplastic marbling material opens onto the wall of the central passage of the extrusion apparatus, i.e. onto the surface of the extrudate made of the thermoplastic base material which is impressed from the screw press into the central passage. The central passage is smooth. The thermoplastic base material which is impressed into this central passage carries with it a twist configuration derived from the screw press. According to the viscosity of the thermoplastic material with which one works the marbling of the product may not completely satisfy requirements. Especially the marbling may not be impressed completely "through and through" the cross section of the extruded profile.